Showing papers by "Jean-Pierre Gattuso published in 1999"

Geochemical Consequences of Increased Atmospheric Carbon Dioxide on Coral Reefs

Abstract: A coral reef represents the net accumulation of calcium carbonate (CaCO3) produced by corals and other calcifying organisms. If calcification declines, then reef-building capacity also declines. Coral reef calcification depends on the saturation state of the carbonate mineral aragonite of surface waters. By the middle of the next century, an increased concentration of carbon dioxide will decrease the aragonite saturation state in the tropics by 30 percent and biogenic aragonite precipitation by 14 to 30 percent. Coral reefs are particularly threatened, because reef-building organisms secrete metastable forms of CaCO3, but the biogeochemical consequences on other calcifying marine ecosystems may be equally severe.

Photosynthesis and Calcification at Cellular, Organismal and Community Levels in Coral Reefs: A Review on Interactions and Control by Carbonate Chemistry

Abstract: SYNOPSIS. Photosynthesis and calcification in zooxanthellate scleractinian corals and coral reefs are reviewed at several scales: cellular (pathways and transport mechanisms of inorganic carbon and calcium), organismal (interaction between photosynthesis and calcification, effect of light) and ecosystemic (community primary production and calcification, and air-sea CO2 exchanges). The coral host plays a major role in supplying carbon for the photosynthesis by the algal symbionts through a system similar to the carbon-concentrating mechanism described in free living algal cells. The details of carbon supply to the calcification process are almost unknown, but metabolic CO2 seems to be a significant source. Calcium supply for calcification is diffusional through oral layers, and active membrane transport only occurs between the calicoblastic cells and the site of calcification. Photosynthesis and calcification are tightly coupled in zooxanthellate scleractinian corals and coral reef communities. Calcification is, on average, three times higher in light than in darkness. The recent suggestion that calcification is dark-repressed rather than light-enhanced is not supported by the literature. There is a very strong correlation between photosynthesis and calcification at both the organism and community levels, but the ratios of calcification to gross photosynthesis (0.6 in corals and 0.2 in reef communities) differ from unity, and from each other as a function of level. The potential effect of global climatic changes ( p CO2 and temperature) on the rate of calcification is also reviewed. In various calcifying photosynthetic organisms and communities, the rate of calcification decreases as a function of increasing p CO2 and decreasing calcium carbonate saturation state. The calculated decrease in CaCO3, production, estimated using the scenarios considered by the International Panel on Climate Change (IPCC), is 10% between 1880 and 1990, and 9–30% (mid estimate: 22%) from 1990 to 2100. Inadequate understanding of the mechanism of calcification and its interaction with photosynthesis severely limits the ability to provide an accurate prediction of future changes in the rate of calcification.

Ultraviolet‐B radiation stimulates shikimate pathway‐dependent accumulation of mycosporine‐like amino acids in the coral Stylophora pistillata despite decreases in its population of symbiotic dinoflagellates

Abstract: Colonies of Stylophora pistillata maintained for four years in indoor aquaria in the near absence of ultraviolet radiation (UVR) contained only small amounts (,5 nmol mg 21 protein) of 10 identified mycosporine-like amino acids (MAAs, which act as UV sunscreens), the largest number reported in any organism. The concentrations of most MAAs increased linearly or exponentially when colonies were exposed to ultraviolet-A (UVA) and ultraviolet-B (UVB) for 8hd 21 in the presence of photosynthetically active radiation (PAR). Total MAA concentration reached 174 nmol mg 21 protein after 30 d, with palythine and mycosporine-2 glycine constituting more than half of the final total. UVB specifically stimulated MAA accumulation: after 15 d, MAA levels in colonies exposed to PAR alone and to PAR and UVA did not differ (7 and 5 nmol MAA mg 21 protein, respectively), while those in colonies exposed to PAR and UVA 1 UVB were significantly higher (28 nmol mg 21 protein). Glyphosate, an inhibitor of the shikimate pathway, eliminated or reduced the UV-induced accumulation of most MAAs during 7 d of exposure, providing the first experimental evidence of their synthesis via this pathway in a coral symbiosis. Densities of zooxanthellae in colonies of S. pistillata, Acropora sp., and Seriatopora hystrix exposed to UVR for 15 d were only one-third of those in control colonies unexposed to UVR. This net decrease in the number of zooxanthellae in the corals (bleaching) occurred despite UV-stimulated increases in algal cytokinesis and in the host cell-specific density of zooxanthellae in hospite, increases that apparently destabilized the symbiosis and caused expulsion of the zooxanthellae.

Measurement of community metabolism and significance in the coral reef CO2 source-sink debate

Abstract: Two methods are commonly used to measure the community metabolism (primary production, respiration, and calcification) of shallow-water marine communities and infer air–sea CO2 fluxes: the pH-total alkalinity and pH-O2 techniques The underlying assumptions of each technique are examined to assess the recent claim that the most widely used technique in coral reefs (pH-total alkalinity), may have provided spurious results in the past because of high rates of nitrification and release of phosphoric acid in the water column [Chisholm, J R M & Barnes, D J (1998) Proc Natl Acad Sci USA 95, 6566–6569] At least three lines of evidence suggest that this claim is not founded First, the rate of nitrification required to explain the discrepancy between the two methods recently reported is not realistic as it is much higher than the rates measured in another reef system and greater than the highest rate measured in a marine environment Second, fluxes of ammonium, nitrate, and phosphorus are not consistent with high rates of nitrification and release of phosphoric acid Third, the consistency of the metabolic parameters obtained by using the two techniques is in good agreement in two sites recently investigated The pH-total alkalinity technique therefore appears to be applicable in most coral reef systems Consequently, the conclusion that most coral reef flats are sources of CO2 to the atmosphere does not need revision Furthermore, we provide geochemical evidence that calcification in coral reefs, as well as in other calcifying ecosystems, is a long-term source of CO2 for the atmosphere

A novel culture technique for scleractinian corals: application to investigate changes in skeletal δ18O as a function of temperature

Abstract: A novel experimental protocol is described that assists investigations of the effect of environmental parameters on records from the carbonate skeletons of scleractinian corals. It involves the culture of coral colonies on glass slides so as to time the skeletal deposition and environmental records precisely. The value of the technique is demonstrated via calibration of the relationship between skeletal δ 18 O and seawater temperature in 2 species of coral obtained from the Gulf of Aqaba. Colonies were grown at 5 temperatures between 21 and 29°C. For Acropora sp. this relationship gave a slope of -0.27‰ °C -1 , a value close to previous estimates. The δ 18 O signature of Stylophora pistillata displayed a high variability between colonies and gave an average slope much lower than previous estimates (-0.13‰ °C -1 ). These data may indicate a taxonomic difference and the need to re-examine the systematics of this genus. Nevertheless, such variability in colonies of a single species or of a set of closely related species may have implications for the use of coral skeleton as proxy records.

Effect of small variations in salinity on the rates of photosynthesis and respiration of the zooxanthellate coral Stylophora pistillata

Abstract: This paper deals with the effect of a long term (3 wk) change in salinity (increase or decrease of 2 to 4 psu) on the rates of photosynthesis and respiration of the zooxanthellate coral Stylophora pistillata. Colonies were exposed to 4 levels of salinity (34, 36, 38 and 40 psu, with 38 psu as the control salinity) and results were compared using I-factor ANOVAs. Salinity had a significant effect on the protein concentration. It was 30% higher at 38 psu than at the other salinities. It had also a significant effect on the rates of photosynthesis, respiration and on the P-g:R ratio. Gross maximal photosynthetic rates were 50% lower at 34, 36 and 40 psu than at 38 psu. The P-g:R ratio was always higher at the control salinity. Most of the colonies maintained at 40 psu died, and this was explained by a very low P-g:R ratio (<1). S. pistillata is therefore especially sensitive to small changes in salinity and seems to acclimate more easily to hypo- rather than to hypersaline conditions.

Measurement of oxygen metabolism in open-top aquatic mesocosms:application to a coral reef community

Abstract: A new experimental and analytical protocol enabling the measurement of the metabolism of aquatic communities in open-top mesocosms is described. It involves estimation of air-water gas exchange and use of a polynomial regression to estimate metabolic parameters from measurements of dissolved oxygen concentration. Sample data is provided for a coral reef community. Its major advantage compared to the standard respirometry technique is that the community is not subject to great variations of physical and chemical parameters such as dissolved oxygen concentration or pH during the experiment. Changes in the concentration of dissolved oxygen were measured over 24 h periods and used to derive community gross photosynthesis (P g ) and respiration (R). Experiments performed on the same community with 2 differents light intensities (360 and 250 μmol m -2 s -1 ) provided consistent estimates of P g (208 ± 50 and 73 ± 20 mmol O 2 m -2 d -1 ) and R (-219 ± 55 and -79 ± 29 mmol O 2 m -2 d -1 ). The air-water oxygen transfer velocities, K O2 , varied between 34 ± 5 and 84 ± 12 cm h -1 . This approach provided estimates of community metabolism that are not significantly different from those obtained using the standard respirometry technique.